Rolling mill employing non-variable prestressing

ABSTRACT

In a rolling mill in each upright there is provided a first hydraulic jack forming part of a hydromechanical clamping system and a pair of second hydraulic jacks forming part of a prestressing device. One side of a cylinder of a plunger piston jack also forming part of the hydromechanical clamping system communicates with the pressure chamber of the first hydraulic jack, while the other side of said cylinder is in continuous communication with the pressure chambers of the second hydraulic jacks associated with the same upright.

United States Patent 1191 1111 3,733,87 Diolot 1 May 22, 1973 54] ROLLING MILL EMPLOYING NON- 3,578,766 5 1971 Diolot ..100 170 VARIABLE PRESTRESSING 3,673,843 7 1972 Diolot.... ..72 245 3,533,255 l0/1970 Sims ..72/8 [75] Inventor: Lucien Diolot, Neuilly, France [73] Assignee: Societe Nouvelle Spidem, Paris, Primary 'f P Mehr France Attorney-Edwin E. Grelgg [22] Filed: Oct. 28, 1971 [57] ABSTRACT pp 193,355 In a rolling mill in each upright there is provided a first hydraulic jack forming part of a hydromechanical 3 F i n ti 1 D clamping system and a pair of second hydraulic jacks 0] ore App ca on Pr on y am forming part of a prestressing device. One side of a Oct. 28, 1970 France ..7038962 cylindcr of a plunger piston jack also forming part Of the hydromechanical clamping system communicates [52] US. Cl ..72/245 with the pressure chamber of the first hydraulic jack, [51] Int. Cl. ..B2lb 31/32 while the other side of said cylinder is in continuous [58] Field of Search ..72/245,246,8,28; communication with the pressure chambers of the 100/170 second hydraulic jacks associated with the same upright. [56] References Cited 5 Claims, 1 Drawing Figure UNITED STATES PATENTS 3,538,733 11/1970 Diolot ..72/245 Patented May 22. 1973 "IIIIIIIIJIIIIIA' I ROLLING MILL EMPLOYING NON-VARIABLE PRESTRESSING The present invention relates to a rolling mill equipped with a hydromechanical clamping system, with which a prestressing device is very closely associated for the purpose of maintaining the force exerted by such prestressing at a substantially constant and furthermore optimum value.

Devices wherein the systems for the clamping and prestressing of a rolling mill are associated with each other in a predetermined manner have already been described in U.S. Pats. Nos. 3,578,766 and 3,538,733. To the latter there corresponds the First Addition No. 90,470 to French Pat. No. 1,314,562.

In U.S. Patent application Ser. No. 871,905, filed Oct. 28, 1969 and entitled Rolling Method Using Prestressing, now U.S. Pat. No. 3,673,843, there is described a rolling mill of this type which is characterized notably in that its rigidity may be substantially increased due to a working process known as the blocked prestressing process.

It has been found that if for the rolling of flat products one of the devices described in the last-named patent is used together with the aforenoted prestressing process as described in the same patent, the variations or deviations in the values to be regulated remain generally small. Consequently, the corresponding regulation system may readily be controlled either manually or with the aid of a motor of moderate power. However, in this particular case since the rigidity of the rolling mill has been improved by a substantial increase in the prestressing force in the course of a continuous manufacturing process (during which, due to wear or expansion, relatively substantial variations in the roll diameters may be produced), a slow but nevertheless perceptible increase occurs in the stroke of the prestressing jacks and, consequently, in the value of the corresponding force, because it is necessary to maintain the spacing between working rolls at a predetermined value. The result of this is that during the course of the rolling process, the force required of the control means becomes progressively more considerable, so that manual control may be found to be impossible and the electromechanical control, in turn, requires the employment of motors of comparatively high power.

It is the object of the present invention to provide an improved rolling mill of the type mentioned hereinabove to obviate, among others, the disadvantage discussed.

The rolling mill according to the present invention has the same fundamental elements as those of the rolling mill disclosed in U.S. Pat. No. 3,578,766. Thus, in the first place, for each machine upright there is provided a main clamping jack associated with a plunger jack of small section and long stroke, in such manner as to maintain captive a constant quantity of fluid within the volume constituted by the pressure chamber of the clamping jack, the working chamber of the plunger jack and the conduit system interconnecting these two chambers; in the second place, the rolling mill comprises, in each stand, a system of prestressing jacks constituted, for example, by two identical jacks disposed between the backing-up chocks.

According to the invention, a first modification introduced into the machine thus defined consists in interconnecting the two pressure chambers of the prestressing jacks associated with one and the same upright.

Further, according to the invention, the common space thus obtained is connected, by means of a conduit system of suitable section, to the pressure chamber of the plunger jack associated with the same upright. Finally, to the last-named conduit system there is connected an external pressure source which may be isolated at will from the conduit with the aid of blocking means.

Apart from the novel arrangement of the various means for actuating the rolling mill discussed hereinabove, the invention makes it possible to define a relationship between the sections of the pistons of the various jacks involved in the regulation of the rolling mill, in such manner as to optimize and, at the same time, render constant the prestressing force to be exerted.

For a better understanding of the invention, the developments to follow will be based on the detailed description of a preferred, although exemplary embodiment of the invention, taken in conjunction with the sole FIGURE which schematically shows one of the machine uprights and the clamping means associated therewith. Reference numeral 1 designates the machine upright (or stand) containing the rolls 2 and 3 and also their chocks 4 and 5; 6 designates the main clamping jack, 7 and 8 the prestressing jacks.

It is apparent that this arrangement, relating to a twohigh rolling mill may, in the same manner, be applied to any other type of rolling mill.

Reference numeral 9 designates the plunger piston jack, which is of small section and has a long travel and which is associated through a first conduit means 13 with the clamping jack 6. The jack 9 is subjected, as known, to the action of a regulating device, for example, an electromechanical device (not shown).

According to the invention, the pressure chambers of the jacks 7 and 8 are hydraulically interconnected by a second conduit means 14 and are connected with the cylinder of the jack 9 by a third conduit means 15. A source of external pressure 10 communicates with the conduit means 15 through a fourth conduit means 16. The said source may, however, be isolated from the conduit means 15 with the aid of a blocking means 11 disposed in the conduit means 16.

The FIGURE also shows three elastic chains in the upright representing three force paths, as explained in detail in the aforenoted U.S. Pat. No. 3,673,843. Thus, the long chain I extends from the, points A and B and passes successively through a portion of the upper chock 4, a fixed wedge 12, the upper horizontal beam of the stand 1, the vertical part of the stand 1, the lower horizontal beam of the stand 1, the clamping jack 6 and finally, a portion of the lower chock 5. The short chain II extends only through the two chocks 4 and 5 and the associated prestressing jacks 7. It is noted that for both chains 1 and II symmetrical traces (not shown) pass through the opposite half of the same components l-8 and 12. With regard to the chain III, it is rectilinear and extends through the rolls 2, 3 and the metal undergoing treatment.

For the mathematical derivation set forth hereinafter, the following definitions are given:

K1 is the yielding coefficient of the long chain 1,

K2 is the yielding coefficient of the short chain ll,

K3 is the yielding coefficient of the rolls and metal chain Ill,

h is the distance between the points A and B common to the three chains,

AL is the momentary displacement of the plunger jack 9,

s1 is the total section of the working chamber at one side of the piston in the jack 9, i.e., of a first compartment of the said jack which is permanently associated with the pressure chamber of the jack 6,

Z1 is the section of the latter chamber,

s2 is the section of the working chamber at the other side of the piston in the jack 9, i.e., of a second compartment of jack 9 and is equal to sl reduced by the section of the rod of said piston; said second compartment is permanently associated with the pressure chambers of jacks 7 and 8,

Z2 is the section of the assembly of the two pistons of the prestressing jacks located in the same upright and interconnected in parallel and connected to that side of the pressure chamber of the jack 9 in which the active section of the piston is s2,

rl =(s1/Zl) is the ratio of the hydraulic reduction between the hydromechanical regulation and the clamping,

r2 =(s2/Z2) is the ratio of hydraulic reduction between the hydromechanical regulation and the prestressing.

Having established these definitions, the invention will refer more particularly to the last two, i.e., to the ratios rl and r2; according to the invention, it is required to make these two ratios equal to each other. This will make it possible to determine one of the sections of the pistons involved, if the three others are known.

Qualitatively, it becomes possible to appreciate the justification of the selection thus made and the consequences thereof on the basis of the considerations following hereinbelow.

It is known, notably from US. Pat. No. 3,673,843

that, during the clamping of the rolling mill under load,-

the variations designated AFl AF2, AF3 which pertain to the respective forces F1, F2, F3 and which are generated in the three elastic chains of the rolling mill are interrelated according to the equation h =(AL/rl) AFl- K1 since the displacement AL must be reduced r1 times, but must be decreased by the yield value AFl K1 of the chain I.

In the chain II, the following equation applies:

L =(AL/r2) AF2 K2 Finally, in the chain III, in the absence of external forces A h=AF3 K3 Proceeding from formulas (a), (b), (c) and (d), after elimination of Ah, AL and AF3, one obtains The preceding expression is greatly simplified if it is assumed that Knowing the yielding coefficients K1, K2, K3 of the three chains I, II, III, the foregoing formula expresses the variations in the prestress F2 as a function of that of the force Fl produced in the chain I.

Now, in practice, the two coefficients K1 and K2 may be considered as being of the same order of magnitude; thus, their ratio may be considered to be I. It thus follows that a given variation AFl causes a variation AF2, the magnitude of which is inversely proportionate to the yielding coefficient K3 of the chain III.

This amounts to saying that, for a value of K3 sufficiently high to be considered as practically infinite, the prestressing force F2 will remain constant during a given operation, even though the clamping force Fl must vary.

The result arrived at by the foregoing derivation may be realized in practice by the particular arrangement proposed by the invention and by the judicious selection of the sections of the various jacks employed.

It is self-evident that if, using the same arrangement, equality between the ratios rl and r2 is not achieved entirely strictly, the practical results achieved will exhibit a certain deviation relative to those obtained under the optimum conditions, the corresponding deviation being the smaller in proportion as it is brought nearer to the said optimum conditions.

A further important advantage of the invention is that it thereby becomes possible to control, by a single manipulation, i.e., by manipuiation of the control rod of the plunger jack piston 9, the entire regulation of the machine. In fact, control is obtained of the closure of the blocking means 11 isolating the pressure source 10 from the connecting conduit between the prestressing jacks 7, 8 and the plunger jack 9; on the other hand, as known from French Pat. No. 1,213,820, which relates to hydromechanical clamping, single and adequate manipulation for simultaneously controlling regulation of the two rolling mill uprights is achieved. Thus, the said single manipulation also suffices in the case of the improved rolling mill according to the present invention.

Yet, a further advantage afforded by the invention is as follows.

The prestressing force F2 is exerted on the upstream face of the piston of the jack 9, in the same direction as the force normally exerted on this same face due to the regulating manipulation. Thus, it thereby becomes possible to reduce the force required by the said manipulation, i.e., to reduce the power of the associated control motors by the magnitude corresponding to the prestressing force F2.

It will be possible, without departing from the scope of the invention, to modify some arrangements thereof or, alternatively, to replace some means described with reference thereto by equivalent means.

What is claimed is:

1. In a rolling mill employing hydromechanical clamping and prestressing and being of the known type that has (a) a plurality of stands, (b) at least two rolls, (c) a chock held in each stand to support each end of each roll, (d) a main clamping jack incorporated in each stand for urging said rolls towards one another and including a pressure chamber, (e) a piston plunger jack of small section and large stroke and including a hydraulic cylinder and a piston movable therein, (f) first conduit means for maintaining communication between said cylinder and the pressure chamber of said main clamping jack, (g) hydraulic fluid of constant quantity maintained captive between said jacks, (h) at least two prestressing jacks incorporated in each stand between the chocks held therein to exert a separating force thereto, each prestressing jack including a pressure chamber, (i) means supplying hydraulic fluid under pressure to the pressure chamber of each prestressing jack, (j) blocking means for arbitrarily isolating said means supplying hydraulic fluid, the improvement comprising (A) second conduit means for maintaining communication between the pressure chambers of said prestressing jacks associated with the same stand and (B) third conduit means for maintaining communication between the pressure chambers of said prestressing jacks and the cylinder of said piston plunger jack for maintaining the prestressing force of said prestressing jacks at an invariable magnitude.

2. An improvement as defined in claim 1, said piston dividing said cylinder into a first compartment and a second compartment, said first compartment communicating with the pressure chamber of said main clamping jack through said first conduit means and said second compartment communicating with the pressure chambers of said prestressing jacks through said third conduit means.

3. An improvement as defined in claim 2, wherein the ratio of the section of said first compartment to the section of the pressure chamber of said main clamping jack and the ratio of the section of said second compartment to the total section of the pressure chambers of said prestressing jacks are substantially equal to one another.

4. An improvement as defined in claim 1, including a fourth conduit means maintaining communication between said means supplying hydraulic fluid under pressure and said third conduit means.

5. An improvement as defined in claim 4, wherein said blocking means is disposed in said fourth conduit means. 

1. In a rolling mill employing hydromechanical clamping and prestressing and being of the known type that has (a) a plurality of stands, (b) at least two rolls, (c) a chock held in each stand to support each end of each roll, (d) a main clamping jack incorporated in each stand for urging said rolls towards one another and including a pressure chamber, (e) a piston plunger jack of small section and large stroke and including a hydraulic cylinder and a piston movable therein, (f) first conduit means for maintaining communication between said cylinder and the pressure chamber of said main clamping jack, (g) hydraulic fluid of constant quantity maintained captive between said jacks, (h) at least two prestressing jacks incorporated in each stand between the chocks held therein to exert a separating force thereto, each prestressing jack including a pressure chamber, (i) means supplying hydraulic fluid under pressure to the pressure chamber of each prestressing jack, (j) blocking means for arbitrarily isolating said means supplying hydraulic fluid, the improvement comprising (A) second conduit means for maintaining communication between the pressure chambers of said prestressing jacks associated with the same stand and (B) third conduit means for maintaining communication between the pressure chambers of said prestressing jacks and the cylinder of said piston plunger jack for maintaining the prestressing force of said prestressing jacks at an invariable magnitude.
 2. An improvement as Defined in claim 1, said piston dividing said cylinder into a first compartment and a second compartment, said first compartment communicating with the pressure chamber of said main clamping jack through said first conduit means and said second compartment communicating with the pressure chambers of said prestressing jacks through said third conduit means.
 3. An improvement as defined in claim 2, wherein the ratio of the section of said first compartment to the section of the pressure chamber of said main clamping jack and the ratio of the section of said second compartment to the total section of the pressure chambers of said prestressing jacks are substantially equal to one another.
 4. An improvement as defined in claim 1, including a fourth conduit means maintaining communication between said means supplying hydraulic fluid under pressure and said third conduit means.
 5. An improvement as defined in claim 4, wherein said blocking means is disposed in said fourth conduit means. 